Electronic switching circuit



June 8, 1954 w. T. REA 2,580,777

ELECTRONIC SWITCHING CIRCUIT Filed Sept. 28, 1950 6 Sheets-Sheet 1INVENTOR. w/z. ro/v r. em

ATTORNEY June 8, 1954 w. T. REA

ELECTRONIC SWITCHING CIRCUIT 6 Sheets-Sheet 2 Filed Sept. 28, 1950 Ll mxm Eg A ME IN V EN TOR W/L 701V 7'. RE 14 A TTORNEY W WRFERWW June 8,1954 W. T. REA

Filed Sept. 28, 1950 ELECTRONIC SWITCHING CIRCUIT 6 Sheets-Sheet 3INVENTOR. W/L 701V 7'. R514 ATTORNEY June 8, 1954 w, REA I 2,680,777

ELECTRONIC SWITCHING CIRCUIT Filed Sept. 28, 1950 6 Sheets-Sheet .4

HI, INVENTOR.

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% ATTORNEY June 8, 1954 w REA 2,680,777

. ELECTRONIC SWITCHING CIRCUIT INVENTOR. z WILTON r REA 5 June 8, 1954 wT. REA 2,680,777

ELECTRONIC SWITCHING CIRCUIT Filed Sept. 28, 1950 6 Sheets-Sheet 6INVENTOR PV/LTON 7: 54

BY I ATTORNEY time.

Patented June 8, 1954 UNITED STATES 2,680,777 ELECTRONIC SWITCHINGCIRCUIT Wilton T. Rea, Manhasset, N. Y., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication September 28, 1950, Serial No. 187,330

. 24 Claims.

.This invention relates to an electronic switching system and, moreparticularly, pertains to electronically operated distributors orcommutators for electronic switching circuits.

The invention is particularly applicable to the transmission oftelegraphic signals, and to the interpretation of the transmittedsignals at the receiver.

According to the' invention, a cyclic switching system, or distributor,is composed of a plurality of thermionic discharge devices which, forsimplicity, will be called distributor tubes; dis-, tributor tubes areassociated with individual signal sources. It is the duty of thedistributor to provide a cyclic connection from each of the signalsources associated with the individual distributor tubes to a commonline for a given interval of time. The time interval over which adistributor tube connects the associated signal source to the commonline is called a distributor segment.

The distributor tubes are individually controlled by a source ofoscillatory potential provided with output terminals from which may bederived a plurality of alternating control voltages difiering from eachother by fixed phase angles. The distributor tubes have one or morecontrol elements which are connected to these terminals through discreteimpedance networks having certain values; during one cycle of the sourceof oscillatory potential, each tube will be rendered conductive for aninterval of time equal to the segment desired at that distributor tube.The segment width, or time during which any one tube is renderedconductive, is a function of the combination of alternating controlvoltages utilized and the impedance network through which these voltagesare appliedto the control elements of that one distributor tube. Thesegments or conductive periods of the various distributor tubes may berendered of equal or unequal time width; they may be made successive oroverlapping in time; and maysucceed one another with or withoutintervening time intervals, dependent entirely upon-the choice ofalternating control voltages and the impedance networks cooperating withthe individual distributor tubes.

The art of communication has employed "distributor switching circuitsfor sequential .synthesis and analysis of a group of signals inorderthatthe intelligence contained therein might be transmitted over asingle line. Signal transmission systems employing such distributors areoften called time division systems. In the past, me-

chanical distributors having a plurality of contact segments have beenutilized. Each of the segments of such distributors is connected to asignal source, and a slider arm or other means is provided to makesequential contact with the various segments, sampling the signal ofeach segment for a short and measured period of Such a distributor isshown in United States Patent No. 1,566,295, to E. F. Watson, issuedDecember 22, 1925. It is known also to perform such an operationelectrically by the use of sequentially self-energizing multivibratorrings as in copending United States application Serial No. 128,395,filed November 19, 1949, by A. Weaver, now U. S. Patent No. 2,626,994,dated January 27, 1953.

To explain the invention more fully, one embodiment of a distributoraccording to the invention will be described as applied to a telegraphicsystem. In one telegraph system, it is known to provide transmitting andreceiving systems employing transmitting and printing equipment of thestart-stop type, utilizing a rotary mechanical transmitting distributorcontrolled by a perforated tape and a rotary mechanical receivingdistributor for controlling a selector mechanism. Such a machine may beof the type described in United States Patent No. 1,904,164, to S.Morton et al., granted April 18, 1933.

Such start-stop automatic telegraphic systems have employed mechanicaltransmitters operated by means of the aforementioned perforated tape,transforming the tapes perforations into groups of electrical impulses.These impulses are transmitted by time division via a transmissionmedium or line to some remotely located receiving position. Suchtransmitting apparatus is described in United States Patent No.2,055,567, to E. F. Watson, granted september 29, 1936. At the receivingposition, the impulses are interpreted. and the letters or symbols to betransmitted are thereupon caused to be printed.

While the example, to which the distributor of the invention is applied,utilizes transmitting and printing equipment of the start-stop type, itis to be understood that such equipment is shown for the purpose ofillustration only. The distributor, according to the invention, is notlimited to transmitting and printing telegraphic equipment or totelegraphic equipment, but is applicable generally to communicationsystems of the time division or multiplex type, to electrohic switchesand selectors, and to telemetering and synchronizing circuits generally.

The principal object of the invention is to provide a cyclic electronicswitching system having segments of equal or unequal time width,successive or overlapping in character, and succeeding one another withor without intervening time intervals. In accordance with another aspectof the invention, means are provided to transmit and receive timedivision telegraph signals with cyclic switching system.

The invention is described in detail in the following specification:

Fig. 1a shows a simplified equivalent schematic circuit of a switchingsegment, included for the purpose of explanation;

Fig. 1b is a timing diagram of the circuit of Fig. 1a;

3 Fig. 1c shows a schematic diagram of one switching segment inaccordance with the invention;

Fi s. 2a, and 2b are equivalent diagrams of the phase shifting networkaccording .to the invention included for the purpose ofillustration;

Fig. 3 shows a schematic circuit-diagram of a switching distributor inaccordance with-the invention;

Figs. 4a, 4b and 4c are Ltiming .and' wave tiform diagrams to aid in theexplanation of the-circuit shown in Fig. 3;

Fig. 5a shows a telegraphic tape sensing mechanism which may be used inconjunction with the telegraphic system according to the invention;

Fig. 5b shows a detailed 'viewof aportion of the mechanism of 5a.

Fig. 6 shows a schematic circuit diagram of a telegraph transmitteraccordingto theinvention;

Figs. 7a and 7?) show a schematic circuit diagram of a telegraphreceiverin accordance'w'ith the invention;

Fig. 8 shows the interrelation-of Figs. 6,712 and 7b; and

Fig. 9 shows a gate selector circuit utilized in Fig. 7b.

Throughout the specification, batteries are indicated as sources ofdirect-current potential. It will be obvious to one skilled in the'art'that such sources may be alternating-current -rectifiers, or asingle rectifier or battery in conjunction with appropriate voltagedividers wherenecessary.

Referring now to Fig. 1c, there is shown a thermionic discharge tube Ihaving a cathode, anode and two control elements-or grids 'A'and B. Eachof the control grids A and B is'capable of arresting theanode-cathodecurrent flow :of

the tube.

It is assumed that a voltage -E' is developed by voltage source 4athrough a resistance 5a to grid A. The resistance 511 may beconsidered-to have a. value R and:

w=21rf t=time; and a is a constant phase angle.

Similarly, a voltage E is supplied .from .source -4b resistance b togrid B, where:

The magnitude value of Equation 2 is exactlythe same asEquation 1 withthe exceptionthat anew constant phasev angle,,.0b, .is introduced.

Voltages E .and B" .will be .identicalin .wave form and .magnitude,difiering only in phase. This phase difierence will be 180 degrees,because of the negativesign of voltage E", with an additionaldifierencafln, due to the difference. between the constant phase angles.05 and 9b.

The energizing circuitsof thetube I ,maybe arranged so thatitsanode-cathode current .will be cut oil during all negative excursionsofthe voltage E. Thus, for oneehalf ofeach cycle of the sine wave ofEf,-the tube will .be non-conducting and during the subsequent half.cycla'will be capable of conducting.

Referring to Fig. 1b,.if the circle represents a single sine wave cyclestarting at 6a as (l, anexcursion of 211' radians of the voltage .E willhave the upper portion of the circle representative of the first halfcycle of the sine wave E. .151 will 4 .;be .positi-ve "over this :half'cycle. The vertica11y shaded ,portion .then i represents .the angularperiod when control grid A permits current to flow.

Similarly with control grid B, negative excursions of the voltage Eprovide periods when the tube I cannot conduct, positive excursions ofgrid B providingzpossible periods of conduction. 'It'has beennoted thatthe expressions for voltages E and E" difier from each other in that:thesexpression.ofrvoltage E" is negative, or shift- .ed nr radians andalso includes an additional phase angle difference,u:0A.

.Ihe conductive period oilered by the control gridjBis showniniFig. 1b,the conductive period being advanced 1r radians over the conductive'period of control grid A by virtue of thenegative sign of voltage'E",plus-an additional phasedisplacement, HA, causedby the difierence in,phase angles .Ba and 0b. The total .part of .the cycle in which controlgrid B will permit currentjflow is represented by the horizontallyshaded .por-

' Examination of Fig. lb "shows that the .only period of time'duringwhich anode-cathode current canfiowjintube Iis thatsector of'time wherethe conductive possibilities of the control grids A and B coincide. Thissector coincides with the phase angle difierence between the twovoltages, on. At all other times, either grid A, gridB or both gridswillblock thepfiow of current,.and'tube I will*remain non-conducting.

By shifting-the phase angle diiference, umbetween 0a and 6b, the sectorof conductionmay'be controlled and the corresponding time over whichtube I will draw 'anode cathode current may be lengthened or shortened.By exciting the grids A'and B of the tube I between the-point ofseturation and cut-off, depending upon vthe voltage-of the gridcycle,a"substantially square :wave voltage may "be obtained. "Thisexcitation-may be controlled, inter alia, by manipulation of themagnitudes of battery; 2 and resistance 3. Thus.a-voltage'will-appear-atterminals;Band g'I inversely proportional to theanode-cathode current drawn by tubeI; during the times tube Iisnonconducting, the voltage at terminals 6 and I will substantiallyequal the voltage of battery "9. When'tube "I conducts, theanodecurrentof the tube produces a voltage drop across resistance 8, depressing-thevoltage at terminals 6 'and I. Asthe tubegoes through thecycle ofnon-conduction, conduction and non-conduction, "a wave, havingsusbtantially a square envelope, willbe generated-attheterminals 6 andI.

An. empirical expression for -vo1tage, V, "supplied -to control grids Aand B, couldbe:

Va V2 Essin (wt-F6) Generator-resistance combination I0 and 'II, havinga circuit-as sh0wn=in Fig. 2c;may---be -assumed to develop this voltage.The voltage, V, produced jby the generator-resistance =combina tion ofFig. Zacan be shown to be identical with a voltage generated by thecircuit "configuration .ofi-Fig52b. To support this identity,-specificrela- .tive values "for generators i2 and I3 and for -resistance networkelements R1, R2 and-R3 must be assumed. "In these specific values, thevoltage generatedrbyl 2 will be:

-by :generator I3:

E2=E cos wt (4) Inthese equations, w=21rfand fpisgequalftothe sinusoidalfrequency :of the generator .10 of Fig.

5 2a. An expression for the voltage G between terminals I 5a and IE2)will be found by the principle of superposition to be:

If the circuits of Figs. 2a and 2b are to be electrically identical, theterminals I5a and I5?) must be presented a resistance equal to the valueof the resistance II in the circuit of Fig. 2a. If resistance I I isequal to R, and inasmuch as R1,

R2 and R3 are in parallel, the following equation 4/ R Rz sin (8) Bysubstituting for R1, R2, R3 and E1 and E2 in Equation 6, By providing amultiplicity of distributor tubes, such as I, and driving them withappropriate control voltages through the proper network ele'-- ments,the conduction cycle of the distributor tubes may be discretelycontrolled. The dis tributor tube current flow, thus controlled, may beutilized to provide output pulses of voltage to control auxiliaryswitching or gate circuits. With such circuits, the pulses may beutilized to cause conduction or non-conduction ofa sep=- arate switchingcircuit. A plurality of distributor tubes plus associated gate circuitscan be made to provide segmented and cyclically repetitive switching,akin in result to a mechanical distributor. An example of such adistributor switching circuit will later be described.

A plurality of distributor tube circuits of the type shown in Fig. 1c isto be seen in Fig. 3. In this figure a group of twelve distributor tubesis utilized. It may be assumed that each of the twelve distributor tubeswill cooperate with other circuits to act as a distributor having twelvesegments.

In order that the energizing network associated with any onedistributing segment may be analyzed, the reference numerals of thenetwork elements associated with each of the various segments bear:first, a number indicating to which segment the network element isconnected;

sin 6 cos 0 2 cos 0- cos 0(sin 0+cos 6) 2 sin 01,/ 2 sin 6(s1n 6+c0s 0)Reducing this expression:

[E sin 0 sm wt+E COS 0 cos wt 2- (sin 0-I-cos 6) a {E sin0cos0 cost? sin6 Referring to Fig. 1c, the equivalent circuit of Fig. 2b is shown assubstituted in the control grid circuits of the distributor tube I. Theeffect of generators I2, I3 and I2, I3, acting through network elementsR1, R2, R3 and R1, R2, R2, is the same as the action derived by thegenerator-resistance combination 4a, 5a and 4b, and 5b of the circuit ofFig. 1a. By the inclusion of the circuit of Fig. 2b, however, the phaseangle 0, of the voltage supplied to either of the control grids 2 or 3of the tube I may be varied. As indicated. by the above equations,varying the parairleters of the generator voltages E1, E2 and E1, E2, aswell as R1, R2, R3 and R1, R2 and R3 allows a selection of the phaseangle as and 9b. Consequently, the conducting time of tube I may beselected to occur for any given period of time and at any point in thephase displacement cycle of the basic angular velocity, to.

second, a letter A or B designating arbitrarily that the network elementis associated with one of the two grids of the distributor tubes of thatsegment; and a second number, either 1, 2 or 3, correlating the networkelement to the corre' spondingly numberedsubscript of the analogousnetwork element in the circuit of Fig. 10. Thus, if 3 is the secondnumber in the reference nu meral of the network element, this element isanalogous to R3 of Fig. 10. For example, in Fig. 3, network element 5BIindicates that the network element is in the fifth segment, connected tothe B grid of this segment, and that it is analogous to element R1 inthe circuit of Fig. 10.

Each of the distributor segments may utilize four voltage sources. Thesevoltage sources are numbered I2, I3, I2 and l3, as they correspond tothe similarly numbered sources in Fig. 1c. The ,four voltages can bedefined by the expressions:

of each will be the same.

The voltages supplied from each of the four sources for onerepresentative cycle have been plotted in Fig. 4a. The voltage derivedfrom volt-' age source I2, E1, may be assumed to be a sine:

7. waveihavingaaznode atitimfii =9. Similarly, enorator. l 3.: will;produce E12,. a cosine; Wave; having a loop: attimez-O. Voltage source.[2' delivers avoltage Er', 1r radians out of phase from 12; voltagesource. 13' produces an output voltage E25, rradians outof phasezfromE2;

One-2 object of thedistributor' of Fig. 3 is to provide a group ofvoltage pulses. As stated, theservoltage pulses-may, in turn, be usedtoenergize. switching, circuits. To-this extent, the voltage? pulses and.the. circuits which generate them maybe consideredas segments in adistributor cycle.-

Eonthe-purpose of illustration, arbitrary segmenttwidths-andsegment-phase occurrences have been chosen. It will be obvious to anyoneskilled in the art that the segment .widths oroocurrences chosen are notnecessarily controlling, but may bewariedby. thezproper manipulation ofthe net.- work. elements and voltages. segments of the: distributor. areshown tobe immediately interjacent. This=arrangement, Sim-.- ilarly, isnot necessary and it is utilized solely for thepurpose of simplicity ofillustration. In this regard, it is possible. to provide. time spacesbetween successive segments or to overlap one ormore successivesegments, providing for a plurality: of operative segments at any giveninstant in the distributor cycle.

The arbitrary segmentation of the distributor cycle is shown in Fig.4?). It is assumed that-at the start of the first segment, S1, the phaseangle ofthe control voltage 01 is at radians. As the source voltagefrequency, f, is assumed here to be the same as the distributor cyclefrequency, the distributor cycle is also at 0' radians. The endof.segment Sr occurs'at 92.. By the same token, the second segment starts.immediately at the end of thepreceding segment ate-z andcontinuesto 63.The segmentation of the distributor will .continue thus, throughsegments S3 through $12. for every given distributor cycle. It is to benoted that the various segments'are. selected to beef random time-width,but-such selection is not-necessary. andthe segments may beequal.

Inconformance with the circuit analysis previouslypresented with regardto Figs. 1a and 1c, appropriate values. of network elementsvcomparableto R1, R2 and R3 of Fig. 1c must be chosen toprovide-thedesired segment phase angles-0.

Similarly,.theproper generator voltages l2, l3, I2 and.l3. must be.selected to pass through-these network elements to oneorthe other gridof the various distributor. tubes.

Four of. the segment phase. angles, 61, 04, 0': and 010, havearbitrarily been chosen toiall. on the quadrantal points 0,

1r and 211- radians, respectively. At these quadrantalpoints, both thesine of a orthe-cosineof 0'- In addition, the

HBEEdiLIIOti be included in. the circuit; Thus. in.

As the sine of 01 is equal to 0' at 0' radians; the resistance value forR2 will be infinite;- andthe corresponding circuit element 1A2 willdisappear. It is obvious that if segment" starts and stops are not madeat the quadrantal points,.the expressions for R1 and R2 will be finiteandnetwork elements corresponding must be provided there"- for.

The network elements of each of the distributor tubes must be evaluatedin accordance with the phase angle of the stopping or starting pointsof. the associated segment. In addition, the proper voltage to besupplied to each of the network elements may also be ascertained. Toprovide a more comprehensive understanding of the distributor circuit ofFig. 3, Table I, as follows, indicates computed parametersofthe-distributor circuits for each of the 12 segments arbitrarilychosen:

Table I Network Network Se Element Network Element Element 5 ReferenceMagnitude Applied No. Voltage 1A1 J? R Esin oz 1A3 2+ E R' E sin wt cos'6:

I l 1132 R E cos wt i sin 8; l i 1 1 2- 2 (sin0z+cos a 2A1 E sin wt cos9:

HR 2A2 sm 6, 5 cosot 2R 2- ficm 9z+cos 82) I 2131 -E"sim.r

cos 0:

WE 9 2Bo Sm 93 Ecos wt 2R I 2133 2- 2 (sin 63+cos0r) I 3A1 47R E'sin uhcos 6;

3A2 Ecos wt sin 6a 3A3 2- 2 (sin fii-l-cos 0a) 382 J? R E'cos mi Withregard to the operation of the distributor of Fig. 3, the first segment,S1, is typical. The voltage applied to the grid 18 of the first segmentdistributor tube will cause this particular tube H to conduct at thepoint 91, which may be seen in Fig. 4b. Arbitrarily, 61 is chosen tooccur at the start or the distributor cycle, where it may be assumedthat time, t, is equal to 0. When, at some period or time later, thedistributor cycle will have reached. a point equivalent to phase angle62, the first segment, S1, will be complete. At this instant, thevoltage applied to the grid 18 will cause the distributor tube ii tostop conducting. Measurement of the voltage between terminal i9 andground will indicate first a negative transition, then a positivetransition of voltage as tube ll becomes conducting and thennon-conducting. As stated, these transitions can be arranged to providea substantially square wave shape with the proper selection of cathoderesistance 20 and cathode bias source 2 I.

At the same instant that the segment S1 is completed, a voltage issupplied to the grid 22 of the tube 23 of the succeeding segment S2. Atthe time that the distributor reaches a point in its cycle correspondinto a phase angle 02, voltages are applied both to grids 22 and 24 whichcause tube 23 to conduct. Conduction of tube 23 continues over segmentS2 until a point in the distributor cycle corresponding to the p ase anle 3 has been reached; at this time, tube 23 becomes non-conducting.

The distributor tubes of each of the succeeding segments S3 through S12will, in turn, conduct. In Fig. 4.0 there is shown a graphicalrepresentation of the anode voltages of the distributor tubes, plottedas a function of time, and labeled in accordance with the segmentationpreviously assumed. For the sake of clarity, the segments bearingeven-numbered subscripts have been shown on separate axes from the oddones. This choice of representation is arbitrary, and the referenceordinate of anode voltage may be the same in each case. In Fig. do, asthe distributor passes from one segment to another, a depression ofvoltage from the reference ordinate will occur,

and this depression may be made substantially a square wave in shape.

The distributor segments will have a width or time value equivalent tothe arbitrary choice made for the various phase angles 6. For ex ample,the segment S7 in Fig. 40 will be proportionately. wider than thesegment S3, depending upon the phase angle difference between $798 and6304.

Telegraph system The distributor circuit according to the invention maybe modified and applied to systems of telegraphic communication and willbe described with reference to such a system. Although described withreference to a telegraph system, it is to be understood that thedistributor circuit and the modification shown are not limited totelegraph circuits, but are applicable to time division transmission andtelemetering systems generally.

In start-stop telegraphic systems, the trans mitters are frequentlyoperated by perforated tape. At the source of the desired intelligence,an operator causes the tape to be perforated in groups representing theletters or symbols to be transmitted. A correspondin group of sensingpins, associated with a tape sensing mechanism, determines the numberand arrangement of the intelligence-bearing signal elements.

perforations representing a given letter or synbol. In the prior art,information received by the sensing pins, 1. e., whether a perforated ornonperforated part of the tape is sensed, was sampled discretely by amechanical distributor system associated with the transmitted equipment.The intelligence found on the relative sensing pins was analyzed by thetransmitting distributor with respect to time. In addition, thedistributor ordinarily transmits a signal element which is used tosynchronize the transmitting and receiving equipment. This system is, ofitself, well known and described in United States Patent No. 2,055,- 567to Watson, granted September 29, 1936. There, in brief, the desiredintelligence is mechanically scanned and then caused to be transmittedin the form of electrical impulses, over a transmission line, to areceiver. The receiver, remotely located, can analyze the receivedimpulses through the provision of a synchronized mechanical distributor.The synchronized distributor includes a selector. magnet energized inaccordance with the received impulses, resulting in a derivation at thereceiver of the originally transmitted intelligence.

Electrical impulses produced as a result of the sensing of theperforated tape are known in the telegraphic art by the terms markingand spacing. Two contrasting conditions of the line are indicated bythese words. In some telegraphic systems, perforation is made to alteror reverse the flow of current in the transmitter medium or line. Insystems employing a reversal of current flow, the line may be said to bein a marking condition when current flow is established in a givendirection, and in a spacing condition when current flow is in theopposite direction. Thus, for a given marking condition, onetransmission line will appear to be positive with respect to the othernegative transmission line; in the spacing condition, these polaritieswill be reversed. A system of this type is known as a polarized system.It will be understood that in other types of systems, the terms markingand spacing may have somewhat different meanings.

In the telegraphic transmitting arrangement, according to the presentinvention, each cycle of distributor rotation will transmit a group offive For each cycle of distributor operation, these five signal elementswill represent the intelligence contained in a particular code group orletter to be transmitted. Synchronizing information essential tomaintain transmitting and receiving equipment in proper relativeoperation requires the addition of synchronizing signals. Thesesynchronizing signals comprise a start signal and a stop signal, andthese mark the beginning and end of each cycle of distributor rotation.

Referring now to Fig. 5a, there is shown a tapesensing mechanism of aknown type, which utilizes a perforated tape 25. Tape 25 may, forexample, be one prepared by a keyboard perforator of the type shown inPatent 1,965,602, granted July 10, 1934, to R. A. Lake or a reperforatorof the type indicated in Patent 1,884,743, granted October 25, 1932, toE. E. Kleinschmidt. The relative positions of perforated andunperforated portions along a given line transversely of the tape travelwill provide various code combinations. As shown, by way of example, asensing pin 26 is received by a hole in the tape 21. The armature 28 andthe contact 29 carried by it are controlled in position by the sensingpin and will 15 mature contacts such as 29 in Fig. a and Fig. 5b. Thesefive distributor tubes will provide discrete and successive pulses tothe armature contacts 29. These, in turn, will connect the distributorpulse to either the marking or spacing contact cooperating therewith,depending upon the intelligence to be read in the perforation groups ofthe tape 25. These distributor tubes 4'l--5l control the time divisionor" the intelligence signals. The synchronizing or start-stop signalsare cared for by a start tube 52 and a stop tube 53. The multigrid stoptube 53, in addition to providing a stop signal, influences a controltriode 54 which, in turn, provides operation of a later-described stepmagnet 33 (Figs. 5a and 6).

- Returning to the intelligence distributing tubes 41 to 5|, theoperation of triode distributor tube 41 is typical. As in the case ofthe tetrode in Fig. 10, two oscillator voltages are supplied to thegrid-cathode circuit of triode 41' through a network comprisingresistances 55, 56 and 51. Resistances 55, 55 and 5? correspond toresistances R1, R2, and R3 of Fig. 1c. The triode 4'1 has only one grid,however; its conduction period will be thus caused to occur over theentire positive excursion of the grid-cathode voltage. The effect ofsuch a single grid control may be seen in Fig. ID, for example, thesector of 11' radians comprising the vertical sectioned area starting atphase angle 99..

"The point in time, with reference to the distributor cycle, at whichthe triode 47 starts its conduction cycle, will be determined by themagnitude of resistances 55, 56, 51 and the alternating voltagessupplied to the resistances 55 and 55. As resistance 55 is connected topoint 4|, there is supplied thereto a voltage having a magnitude E sinwt. The resistance 56 is similarly supplied from point 42 with a voltageE cos wt. By virtue of the network and voltages selected to supply thegrid of 41, a conduction cycle starting at a given phase angle willoccur. Conduction of triode 41 is reflected as a voltage drop in itsanode-cathode circuit; the increased anode current flow throughresistance 58 causes an increased voltage drop across the latter,depressing the voltage at point 59. The transient change in the voltageat point 59, resulting from the change from the conducting to thenon-conducting condition, will be applied through capacitance Bil toarmature contact 29.

Contact 29, it will be remembered, is shown in Figs. 5a and 5b ascontrolled in position by the perforations in the tape 25. Dependingupon whether the armature 28 and its cooperating sensing pin 28 readeither a perforated or an unperforated portion of the tape, the armature29 will be made either to contact 35 or contact 3 I. As shown in Figs.5a and 5b, the sensing pin reads a perforation 21; as a result, contact29 makes with contact 36. The same situation is displayed with regard tothe remaining analogous contacts, as 18, in Fig. 6.

Each of the remaining distributor tubes covering the intelligenceportion of the distributor cycle, i. e., 48-5I, will operatesequentially and in the same manner as clidtriode 4?. In each case, theassociated resistance network comparable to 55, 56 and El or R1, R2, andR3 will have values chosen which, together with the voltages suppliedfrom two of the four voltage source points 4|, 42, 44 and 46, will causethe respective triodes to provide a conducting cycle of substantially 1rradians. The conducting cycle will com- 16' mence at a phase angledependent upon the parameters of the resistance network and voltagesselected. The various distributor tubes will supply sequential pulses ofvoltages to cooperating sensing armature contacts. These voltage pulsesalternatively reach either one of two buses, 73 or '54. It will be shownthat when a negative pulse is received on bus 73, a spacing conditionwill be established on the transmission line between transmitter andreceiver. When a negative pulse is received at bus '14, a markingcondition will be established on the transmission line.

For the purpose of illustration, it has been'as-..

sumed that the start synchronizing signal will reflect a spacingcondition on the line. The spacing synchronizing signal, coming beforethe intelligence portions of the distributor cycle, is provided bytriode 52. Triode 52 is provided with a conduction period starting at aphase angle 0, dependent upon the network comprising resist ances iii,82 and 53 connected to voltage sources from points 4! and 45. As withtriode 41, a negative pulse of voltage will be transmitted throughcapacitance E4 to the spacing bus 13, at the time that the anode-cathodecircuit of triode 52 becomes conducting. This pulse will occur at sometime before the conduction of the various intelligence segments of thedistributor. The grid of distributor tube 52 is supplied from points 41and 4 56. As previously indicated, point 45 will have a residualdirect-current component resulting from the anode supply voltage. Toovercome this unwanted direct-current component, a negative bias source52a, acting through resistance 5211,

' i5 provided, and the component will be eliminated.

At the end of the intelligence segments of the distributor, a stopsignal is produced by the multigrid tube 53. Diifering, however, fromthe other distributor tubes 41-52, tube 53, having two control grids, isprovided with controlled conducting and non-conducting segment points inthe manner of the circuit of Fig. 10. One control grid 68a is suppliedwith voltages from points t2 and 44 acting through'a network comprisingresistances 65, 66 and 61. Similarly, a second control grid 68?) issupplied with voltages from points 44 and 46 through a networkcomprising resistances 69, lo and H. As a result, tube 53 has aconducting period, the beginning and end of which will be controlled byeither of the'two grids 58a and 62 8b and their associated networks andsupply voltages as shown graphically in Fig. 1?). Negative bias sources53a and 53b operate to eliminate the unwanted direct-current componentof the voltages from points 44 and 46, respectively.

In generating the stop pulse, as tube 53 passes from the non-conductingto the conducting condition, a negative voltage pulse will betransmitted through the capacitance 12 to the marking bus 14.

For the purpose of illustration, one division of time between thevarious segments provided by distributor tubes 4l--53 may be described.According to this illustration, the start distributor tube 52 mayinitiate conduction at the O-degree point of the distributor cycle;distributor tube 41 may start conducting at 48 degrees, tube 48 at 97degrees, tube 49 at degrees, tube 50 at 194 degrees, and tube 5| at 242%degrees; tube 53 may start conducting at 291 degrees and stop conductingat 360 degrees. At each of the points at which a tube conduction starts,there will beprovided a negative pulse supplied throughthe cooperatingcapacitance. Although positive pulses result from the completioniof theconducting cycle, the positive pulses are rejected.

In further examination of the distributor cycle, the negative pulsedeveloped through the capacitance 64 by the start of conduction in tube52 is supplied to the bus 13. This negative pulse on the spacing bus '13signals the initiation of the distributor cycle, and is the start pulse.The positive pulsesubsequently received through the capacitance 34 as aresult of the cessation of the conducting of tube 52 travels to theanode of a rectifier 15 and thence .down the space charge path to thecathode thereof and ground. Positive pulses on the bus 13 will all bedissipated in this manner.

As the next step in the distributor cycle, triode 41 becomes conductingat a given instant of time equivalent to the shift in phase angleprovided by the resistance network 55, 56 and 51, and'the voltagessupplied from the points 4! and 42. It has been indicated thatconduction of triode 41 may begin at a point 48% degrees along in thedistributor cycle. In any event, when triode 41 conducts, a negativepulse is transmitted through the capacitance 50 to the contact of thesensing armature 29. Dependent upon whether the contact 29 is madeagainst contact 30 or 3|, the negative pulse is further transmittedeither to the marking bus 14 or the spacing bus 13, respectively. In thetape conditions indicated in Figs. 5a and 5b, as well as in Fig. 6,contact 29 is made with contact 30. As a result, the negative pulse fromcapacitance 60 is transmitted to the marking bus 14. The subsequentpulse developed at the end of the conducting period of the triode 41will not aifect the marking bus '54; all positive pulses thereon will bedissipated by the marking bus damping rectifier 16.

To continue in the distributor cycle, the triode distributor tube 48starts conducting at some later time in the distributor cycle. The startof the conducting cycle oftube 48, which may be at 97 degrees inaccordance with the value assumed for illustration, produces a negativepulse through the capacitance TI. This negative pulse reaches a tapesensing armature contact 18. Under the condition as shown, contact l8reflects an unperforated condition of the tape and is made to contact18a; the negative pulse will therefore be transmitted to the spacing bus13.-

Depending on the reading found on the tape, the subsequent conductivedistributor triodes 49, 50 and 51 will provide negative pulses either tothe spacing or marking buses E3 and T4. The positions for the armaturecontacts, .as 29, are indicated arbitrarily for th purpose ofillustration;

A stop signal coinciding with the initiation of conduction ofdistributor tube 53'is presented through capacitance 12 to the markingbus '14, providing a marking signal; This point, at which distributortube 53 becomes conducting, may be assumed to be at 291 degrees. Thepositive pul e subsequently received from the end of conduction of thetube 53 is absorbed byimarkingbu's damping rectifier l5.

The stop distributor tube 53 fulfills a second function in addition toproviding the marking stop signal to the marking bus 753 as previously dscribed. The pulse, occurring as a result of the transition from thenon-conducting, to conducting, to non-conducting conditionof the tube53, -is coincidentally transmitted to the gridcathode circuit of control'tube 54. Atthe time 18 tube 53 passes from the non-conducting to theconducting condition, assumed to be at 291 de grees in the distributorcycle, the grid of control tube 54 becomes less positive. Until now,control tube 54 has been conducting but the depression of grid-cathodevoltage causes tube .54 to become non-conducting. Relay i9 is operatedby the anode current of tube 54. As the normal condition of tube 54 isconducting, the relay contacts are held open. The initiation of theconducting cycle of tube '53 interrupts the anode current of tube 54,and the relay [9 is deenergized. Upon the termination of conduction oftube 53, assumed to be at the 360-degree point in the distributor cycle,the grid-cathode voltage of control grid 5t will once again rise to itsnormal value, triode 54 again conducts and the relay 19 will beenergized. Energization of relay it causes the armature 19a to bewithdrawn from the associated contact 1%. Contacts 19a and 19b, in turn,open the circuit between a power source, 86, and the coil of step magnet33. When relay 19 is deenergized, reflecting a non-conducting conditionof control tube 54, power supply energizes the step magnet 33,performing its previously described function of rotating the bail 32 ina counterclockwise direction as shown in Fig. 5a. The ensuingoperations, such as the withdrawal of the sensing pins, such as 26, andthe operation of the escapement mechanism 36 driving the tapefeedsprocket 35 as described, will occur. At the completion of theconduction cycle of tube 53, control tube 54will once again conduct,relay coil 79 will be energized, and the circuit of the step magnet 33will again become deenergized, allowing the successive tape sensing anddistributor cycle to begin.

Transmitter gate circuits A series of five negative intelligence pulseshave been shown to appear either on the spacing bus 13 or the markingbus l4, depending upon which of the five cooperating armatur contactsread perforations or nonperforations in the intelligence of perforatedtape 25. Two synchronizing signals also appear; a negative pulse onspacing bus 13 providing the start signal; a

negative pulse on marking bus 14 providing the stop signal. The start,intelligence and stop pulses appear in sequential order on either of theappropriate spacing or marking buses.

These short negative signal impulses must be filled in or interpreted toprovide a variously polarized output toa transmission line pair. Toaccomplish this, there is employed a multivibrator having two conditionsof stability, commonly called a flip-flop circuit. This circuit utilizestriodes 81a and 81b. The energizing circuits of the triodes 81a and 811)are so arranged that if one of the two triodes is conducting, the othertriode must be non-conducting. Assuming, for example, that triode 8ta isconducting, the anode current flow resulting provides a depressed orless positive anode voltage. This less positive anode voltage issupplied through resistances 82b and 83b to the grid-cathode circuit of8lb.

The bias supply source 84?) has a value together with the assumed lesspositive anode voltage transmitted to the grid of tube 8|b that Willbias the latter .to cut-off. As tube Bib is cut off,theanode-cathodevoltageof Bib is at its positive maximum; this positivemaximum voltage is transmitted through resistance 32a and 83a to thegrid-cathode circuit of triode 81a. The value of bias supply Eda is notsufficient to overcome this maximum positive voltage applied to the grid01 Ma; sic will, therefore, continue to conduct. It can be shown that ifthe conditions of stability are reversed, i. e., that fill) isconducting, 81a must become non-conducting, and this new condition willbecome similarly stable.

Alternate conditions of conduction are estab- I lished between thetriodes 8m and 8th by voltage pulses transmitted from the marking andspacing buses. Thus a negative pulse passes through resistance 85a fromthe spacing bus E3 to the grid of triode 81a; pulses are alsotransmitted from marking bus it, through resistance 85b to the grid oftriode Mb. Assuming first that triode tile is conducting and triode 8H)nonconducting, then if a negative pulse is received on the grid of amfrom the spacing bus 73, this pulse, when combined with the voltage ofthe bias source 84a against the positive voltage derived from the anodeof Sib, will arrest conduction of triode 81a. WVhen 81a stopsconducting, the voltage drop across anode resistance 81c disappears andthe anode-cathode voltage rises to a positive maximum. This increasedpositive voltage is transmitted through resistances 82b and 83b to thegrid of triode 81b, overcoming the effect of the negative bias source8%. The triode 8522 will thereupon start conducting. As a result of theconducting condition in triode Bib, its anode-cathode voltage isdepressed by the voltage drop across resistance 81d. The less positivevoltage thus derived is transmitted over resistances 32a and 83a to thegrid of triode 31a and combined with bias source 84a; triode cm ismaintained in non-conducting condition. Thus, even though the initialnegative pulse received from the spacing bus l3 has decayed, the 1 newcondition of stability, wherein 81a is nonconducting and tail) isconducting, will be maintained until a new condition occurs on themarking bus.

When a condition of stability is reached resulting from a negative pulseon the spacing bus 13, subsequent negative pulses on the spacing bus 73will no longer aiiect the grid. of triode Bic. As triode am isnon-conducting, negative pulses on the grid thereof can cause no changein operation; the flip-flop multivibrator will ignore negative pulses onthe spacing bus. To change the condition of stability reached, theremust be a negative pulse on the marking bus l -i. A negative pulse onmarking bus 14 reaches the grid of triode Mb through resistance 85b;triode 8lb will stop conducting in the manner previously described withreference to Gia. A conducting condition thereupon occurs in triode 8to: and will become stable irrespective of the decay of the negativepulse on marking bus 1 To summarize, alternate spacing and markingconditions will cause the multivibrator tubes am and 81b to reach one oftwo conditions of stability, depending upon whether the spacing bus 73or the marking bus 14 last developed a negative pulse.

The alternate conditions of stability of multivibrator tubes 81a and 8H)are utilized to control the amplifier tubes 86a and 88b. The anodevoltages of the triodes 8m and 81b are coupled discretely to cathodefollower amplifiers 85a and 861) through resistances 81a and 811),respectively. If a spacing pulse on bus 73 was last received, thecondition of the multivibrator stability will be such that triode sla isconducting and triode 3H) non-conducting. The anode voltage of am inthis condition will be less positive as previously described; this lesspositive voltage condition is transmitted through resistance 81a to thegrid of triode amplifier 86a. Negative supply 88a overcomes thedepressed or less positive voltage derived from 8m to cause triode 86ato stop con ducting. The non-concurrent conducting condition of triode8th provides a positive maximum of voltage at the anode of the lattertube; this positive maximum voltage is supplied through resistance 87bto the grid of triode amplifier 86b. The negative bias supply 882) has avalue when combined with the positive maximum voltage which will allowtriode 86b to conduct.

As there is no anode-cathode current through non-conducting triode a,there will be no voltage drop across cathode resistance fifia. However,the anode-cathode current drawn by conducting triode 8% provides a givenvoltage drop across the cathode resistance 89b. The combined cathoderesistance voltage drop across Biia and 89b'is applied to terminals 90aand 9012. Measurement of the voltage across terminals a and 98b willreveal a voltage proportional to the cathode current of 8%, terminal961) being positive with respect to Sta. This resultant polarity ofvoltage at terminals 902) and 99a is derived by a pulse occurring onspacing bus 13. A subsequent marking pulse on the bus M will reverse theconduction conditions of amplifiers 86a and 86b previously described;cathode current will now be drawn by triode 86a through cathoderesistance 89a while cathode current of 8533 ceases to flow throughresistance 8%. As a result, the voltage now measured across terminalseta and 99b of the transmission line pair will have a value proportionalto the cathode current flowing through resistance 89a; terminal etc willnow be positive with respect to terminal 98b.

To summarize: The polarity of the voltage recurring across terminals 96aand 581) will alternate with timed successive pulses respectivelyderived on the spacing and marking buses '53 and M. In turn, thenegative pulses obtained on these buses are timed by the controlledcycling of the transmitting distributor, and depend for context upon thereading of the tape perforation intelligence by the tape sensingmechanism of Fig. 5a, together with synchronizing signals forcoordination of the transmitter and receiver.

The terminals 98a and 9% may be coupled to some medium of transmissionsuch as a transmission line.

Telegraph receiver system Figs. 7a and 71), read together, show atelegraph receiver in accordance with the invention.

With reference to Fig. 7a, terminals Qta and Qllb represent terminals atthe receiver to which the remote termination of the transmission mediumor line originating at terminals 90a and 90b of Fig. 6 may be connected.The polarized signals received at terminals sila and S Jb are impressedon the grids of amplifier triodes 94c and 9"). The energizing circuitsof triodes Qla and 91b are arranged so that they will become conductingor non-conducting in an opposed manner, depending upon whether a markingor spacing condition exists upon the line. Thus, when a markingcondition exists at the transmitter, it may be assumed that terminal90'a will be positive with respect to terminal 9I3'b. As the cathodes ofboth triodes 9m and Sib are inter- 21 posed electrically betweenterminals 90'a and 9, by resistances 92a and 92b through ground andresistance 9Ic, the positive voltage applied by 90'a to the grid-cathode9Ia will cause 9Ia to be conducting; the negative voltage applied by SM)to the grid of triode 9 lb will cause 9 Ib to be nonconducting. Underthese conditions the anodecathode voltages of the triodes 9Ia and 9Ibwill be such that point 935 will be at a positive maximum; 93a will beat some less positive voltage. It is to be remembered that these voltageconditions apply when a marking condition occurs at the transmitter. Asubsequent spacing condition received over the transmission medium atterminals 90a and 00'b will reverse the conditions; 9Ia. stopsconducting, 9Ib conducts; 93a reaches positive maximum, point 93bbecomes less positive.

In a telegraph system in accordance with the invention, the receivermay, for convenience, be considered as comprising two fundamental parts:one part comprising the receiver oscillator which may be called thestart-stop oscillator; a second part comprising the receiver distributorand its associated gate circuits. The general plan is for the start-stoposcillator to control the operation of the receiver distributor ring.With the initiation of the start signal sent from the transmitter, thereceiver oscillator is caused to commence operation and will continueuntil the stop signal is received from the transmitter. The receiveroscillator will remain quiescent until a succeeding start signal isreceived. In the excursion of the oscillator during the time between thestart and stop signals, substantially synchronized control voltages areproduced by the oscillator circuits and are impressed on the receiverdistributor ring, causing it to advance. In turn, the receiverdistributor ring opens and closes sequentially a group of cooperatinggate circuits which, in effect, selectively switch the incoming signalto a plurality of receiver channels analogous to the five intelligencechannels provided at the transmitter.

On Fig. 7a may be seen the circuits of the startstop oscillator; in Fig.7b is found the receiving distributor ring and its cooperating gatecircuits. The voltage derived by line amplifiers @Ia and SH: istransmitted simultaneously to the startstop oscillator and to thereceiver gate circuits.

Receiver osc llator The voltage derived from the line amplifiers 9Ia andSI?) at terminals 03a and 93b is transmitted through capacitances 94aand 94b to the cathode and grid, respectively, of oscillator start tube95. To understand properly the function of the oscillator start tube,the oscillator and its associated circuits must first be considered.

Oscillator triode 96 is of the tickler feedback or tuned grid type, withoperation as described with reference to the transmitter oscillator 3'!of Fig. 6. The frequency of the receiver oscillator will depend upon thevalues of inductance 01 and capacitance 98; these should. be such as toprovide a fundamental frequency of the parallel resonant circuit closeto that of parallel tuned circuit 38 and 39 in the transmitter.Oscillation is stimulated by positive feedback to the oscillator gridcircuit from tickler coil 99 in the oscillator anode circuit. Theinductance 9'! will have voltages at the terminus of its Windindiffering y all radians. As in the case of the transmitting inductance38, the grid end I00-of inductance 9! will be assumed to evidence avoltageE sin wt; at the other end, IOI, a voltage E cos wt. The voltageE sin wl'; at point I00 is supplied in part to the grid-cathode circuitof a sine inverter triode 502. As with transmitter sine inverter tube43, Fig. 6, I 02 will have an anode-cathode voltage at point I03 havinga characteristic E sin wt, being displaced 1r radians from the voltageof I00. Similarly, a portion of the cosine voltage at point I GI issupplied to the grid-cathode circuit of cosine inverter tube I04. Aswith cosine inverter tube 45, Fig. 6, the anode-cathode voltage of thecosine inverter tube I04 displays a voltage at point I05 having acharacteristic E cos wt, being displaced 1r radians from the voltage ofpoint I0 I. At points I03 and I05, a direct-current component resultsfrom the residual anode voltage of the inverter tubes. Thisdirect-current component ordinarily requires neutralization in thedistributor circuits.

Thus, at points I00, -III, I03 and I95, there will be found voltageshaving characteristics respectively: E sin wt, E cos wt, E: sin mi, and-E cos wt. These voltages are substantially identical in frequency andwave form to the ones utilized by the transmitting distributor of Fig.6.

The oscillator of the receiver, however, is provided with additionalcircuits to carry out the start-stop feature. The oscillator controltube 95 has its anode-cathode circuit in parallel with the paralleltuned grid-cathode circuit of the oscillator triode. Dependent uponwhether oscillator control tube 95 is conducting or non-conducting, theoscillator 96 will remain quiescent or oscillate by virtue of thepresence or absence of the path presented to the resonant circuit viathe space charge path of the control tube. For example, with a steadymarking condition applied to terminals a and SM) and with theoscillatory circuit in its zero degree condition, a negative potentialat point IOI and an equal positive potential at point I03 will cooperatevia resistors H8 and I06 (the latter having the lower resistance) tomaintain grid I0'Ia. of tube I0! at a positive potential. Likewise, anegative potential at point I00 and an equal positive potential at pointI05 will cooperate via resistors I I0 and I00 (the latter having thelower resistance) to maintain grid I 01b at a. positive potential. TubeI01 will, therefore, conduct and its plate will be at a relatively lowpositive potential. Consequently, tubeI I3 will be biased beyond cut-offby battery I Id acting via resistance I Ida, and its plate will be atfull positive potential. The grid of tube will, therefore, assume apotential positive with respect to its cathode and current will flow inits plate circuit, which includes winding 91. The oscillatory circuit,clamped by the impedance of the platecathode circuit of tube 95, willremain quiescent with energy stored equally in the inductance of winding9'! and in capacitor 90.

When a spacing signal is received at terminals 00'a and 90'b, the formerwillswing toward negative and the latter toward positive. Plate currentfiow will be initiated in triode BIZ) and plate current will cease toflow in triode File. The swing of the plate voltages of these triodeswill. cause a negative impulse to be applied via condenser 94b to thegrid of triode 95, and a positive impulse to be applied via condenser94a to the cathode of triode 95. Current will cease to flow in the platecircuit and the damping effect of said plate circuit will be removed.The energyv 23 stored in capacitor 99 will flow into inductance 91 untilthe voltage across resistor II'I attains a maximum value andsimultaneously, the voltage across capacitor 98 becomes zero.Thereafter, the energy will flow from inductance to capacitance and thusoscillation is initiated.

Before the impulses applied via condensers 94a and 95b to triode 95 haveterminated, the voltages at points IGI and I93 will have progressedsufiiciently far negative to swing grid IBIa beyond cut-on. Said gridwill remain negative until the half-cycle point of the oscillation hasbeen passed, and grid lib, which initially progressed toward positive,will become negative slightly before the half-cycle point ofoscillation. While one or the other of these grids remains negative, theflow of plate current in tube I9! will remain interrupted and the platepotential of this tube will remain at full positive value. Consequently,current flows in the plate-cathode circuit of tube II3, whose platepotential is thereby held only slightly positive. This causes tube 95 toremain out 01f, even though the incoming signal may resume the markingcondition.

Grids Nile and Hllb will not again become simultaneously positive untilshortly before the end of the cycle. When they do, tube I91 con ducts,cutting oil tube H3 and causing tube 95 to conduct. Consequently, at theend of one cycle of oscillation, the oscillator stops and waits for thereceipt or a succeeding spacing signal.

Thus the stop condition of the oscillator is stably maintained over thestop segment as transmitted from the transmitter.

Upon reception of the start signal of the succeeding distributor cyclewhich has been assumed to be a spacing signal, the terminal 9B'b willbecome positive with respect to 99'a. Current will now flow in amplifiertriode 9 l b as a result of the positive voltage thereby applied to itsgridcathode circuit. By the same token, the grid of amplifier triode Siabecomes more negative with respect to its cathode as a result of thechange of terminal polarity; triode 9Ia will stop conducting. Theresultant efiect will be to depress the anode voltage of triode 9i!) andraise the anode voltage of triode am. This will be transmitted to thegrid-cathode circuit of control tube 95 as a negative grid voltagepulse.

The negative grid voltage pulse at control grid 95 causes the oscillatorcontrol tube to cease conducting, unclamping the oscillator triode 99which now will start oscillation. In turn, the voltage at point 509 willbecome less negative, more current will then flow in the sine invertertube I92, and the sine inverter tube anode voltage at point I93 will bedepressed. Initiation of oscillation will simultaneously increase thenegative voltage to be found across resistance Ill, caus ing point IOIto become more negative. This more negative voltage, applied to the gridof the cosine inverter tube I94, increases the anode voltage of thattube, making point Hi5 more positive. The potentials on leads I93 andIll] being less positive and more negative, respectively, act throughresistances I96 and H8 to the grid Ifll'a of the stop tube IN. The stoptube IB'I will have its anodecathode current interrupted as a result ofthe more negative voltage applied to grid iilla. While points I09 andI05 become less negative and more positive, respectively, the resultantmore positive change applied through resistances I98 to H9 to the gridlfl'Ib will fail to maintain or restore the flow of current through thestop tube I01; the control grids are efiectively in series 7 in thespace charge path of I91, and cut-off at grid Illla will control thedischarge path.

Cessation of current flow in stop tube Iill causes a resultant rise inits anode voltage. This rise of anode voltage overcomes the negativevoltage obtained from bias source H4, and the inverter tube IIS willstart conducting. As inverter tube H3 conducts, the depressed anodevoltage resultant is transmitted through resistance I I5 to the controlgrid of the oscillator start tube 95. This less positive voltage, incombination with the negative bias supply H6 operating throughresistance Ilfia, depresses the control grid-cathode voltage of theoscillator start tube to a point at which the oscillator start tubestops conducting; a new condition of stability results. In the newstable condition, the oscillator control tube is held non-conducting;this al lows oscillator tube 96 to provide the desired excursions of sinand cos voltage for the operation of the receiver distributor.

Receiver distributor ring When the oscillator tube 95 commences itsexcursions of voltage in response to the received spacing start signal,sinusoidal voltages will appear at point I00, point l9l, point I03 andpoint I05 and to the connected terminals W, X, Y and Z in Figs. 7a and7?). W, X, Y and Z are supplied respectively with voltages havingcharacteristics E sin wt, E cos wt, E sin wt and E cos wt. In additionto these alternating voltages, residual direct voltages resulting fromapplied anode potentials utilized in the inverter circuits are prescutand must be neutralized when applied to the receiver distributor ring.

The distributor ring tubes, H9 through I23, provide sequentially timedcontrolling voltage pulses for interpretation of the intelligencesignals provided by the transmitter. According to the general plan,receiver gate tubes are opened at instants corresponding to the centersof the segments of the transmitting distributor cycle; the spacing ormarking condition of buses I3 and 14 at these instants will actuate thereceiver gate tubes accordingly. The receiver gates will thereforeprovide an output for each cycle of distributor rotation, selectivelyresponsive to the perforated and unperforated tape readingsrepresentative of the intelligence to be transmitted.

A unique distributor ring tube, I24, will reflect completion of onecycle of receiver distributor operation; will respond with thetransmitted marking stop signal.

The utilization of the output derived from the receiver gates controlledby the intelligence distributor tubes as well as the output of tube I24will later be described.

The operation of any one receiver distributor ring tube will be typicalof all the remaining tubes of the ring. For example, triode II9 providesthe initial response of the receiver distributor after the receivedspacing start signal has set the receiver oscillator into operation. Theoscillator voltages now to be found at terminals W and X, E sin wt and Ecos wt, are transmitted to the grid-cathode circuit of tube H9 through anetwork comprising resistances I25, I26, and I21. It will be noted thatthe latter network is of the same configuration described both withreference to the transmitting distributor ring tubes 47, Fig. 6, thedistributor tubes of Fig. 3, and the circuit of Fig. 10. In common withthese, the magnitudes of resistances -421 are selected together with thevoltages applied thereto 25 to provide a given phase angle 9'1 at whichtube H9 starts to conduct.

In selecting this phase angle 1, the first receiver distributor tube H9should begin to conduct at an instant substantially at the mid-point ofthe first intelligence segment of the transmitting distributor. Thefirst intelligence segment lies in time between the initial conductionof the first intelligence transmitting distributor tube 41, Fig. 6, andthe initiation of conduction of the second intelligence transmittingdistributor tube 48. During this first segment, it has been shown thatthe intelligence to be found by the tape sensing armature 28, i. e., theperforation 2'! of tape 25, is transmitted.

With regard to the transmitter, arbitrary values chosen forthe'initiation of conduction of transmitting distributor tubes 41 and 48were at 48 degrees and. 97 degrees, respectively. While the transmittingand receiving distributors are in substantial synchronization throughthe coordination ofiered by the start-stopsignal and proximity ofoscillator frequencies, slight variations may occur from cycle to cyle.To avoid the possibility that the receiver may misinterpret a receivedsignal, it has been found advantageous to initiate the conduction of thereceiving distributor tubes to coincide in general with a point near themid-point of the segment to be interpreted. This will allow a margin forerror, due to signal distortion and other causes, on each side of thevarious receiving distributor sampling oints. Thus, the phase angle 0'1assigned tothe first receiving distributor tube I I9 may arbitrarily be72%. degrees, the sum of 48 and 24% degrees which are respectivelythephase angle of the start element and the phase angle of the firstintelligence element, thereby coinciding with the mid-point in thetransmitted first intelligence segment.

At the point 0'1 in the distributing cycle, the control grid of thefirst receiving distributor tube I I 9 becomes positive and H9 conducts.Conduction of triode I9 depresses its anode voltage, causing anexcursion toward a less positive potential which is transmitted as anegative pulse through capacitance I28. At a given period of time 1rradians later, the grid of the distributor tube I I9 will becomenegative as a result of theexcursion of grid voltage applied theretofrom the volta e sources of the receiver oscillator; a positive pulsewill be transmitted through capacitance I28.

Similary, negative and positive pulses are produced by the subsequentreceiving distributor tubes IZE, I2I, I22 and I23, at pointsapproximately in the mid-points of the second, third, fourth and fifthintelligence segments of the transmitting distributor cycle, andresultant negative and positive pulses will be transmitted respectivelythrough capacitances I29, I39, I3I and I32. Arbitrary mid-point valuesfor the various values of angles, at which the distributor tubes I29 toI23 start conducting, are: 121 degrees, 169% degrees, 218 degrees and266%. degrees from the beginning of the distributor cycle.

Receiver gate: tubes Receiver gate tubes controlledby the receivingdistributor ring are shown in Figfi'lb as I33ct and. b through I3'Ia andb. A detailed analysis of the operation of these novel gate circuits,which also actto store intelligence, may be made with reference to Fig.9.

In Fig. 9, a multivibrator .having two conditions of Stabllitycomprisestriodes 133a and I337). At any given time when one of the triodes, forexample I33a, is conducting, the other triode I332) will benon-conducting. The alternate condition of stability finds triode I331)conducting, I33a non-conducting. Assuming, for'illustration, that triodeI331; is conducting, the anode voltage of this triode will be-depressedby the voltage drop across resistance I38a. This depressed voltage willbe transmitted through resistance I3Sa to the grid of triode I331). Thedepressed anode voltage reacts with a negative voltage derived from biassource 1581) operating through bias resistance IMb. Assuming for themoment that these are the sole voltages supplied to the grid of 1331),the energizing circuits of triode I331) have values at which thedepressed anode voltage of triode I330; will reflect as a negativevoltage below cut-off in the grid-cathode circuit of triode I33b. Thus,the triode I331) remains non-conducting; the anode voltage of the lattertube will remain at a positive maximum. In turn, this positive maximumvoltage is transmitted through the resistance I392) to the grid oftriode I33a, where it will react'with a negative voltage from biassource I40a operating through bias resistance I Ma. The energizingcircuits of the triode I330. have values at which the positive maximumof voltage derived from the anode of triode I332; reflects as a positivevoltage above saturation at the grid-cathode circuit of triode I33a.Triode I33a. will therefore besustained in the conducting condition.Thus, until other factors intervene, the triode I33a remains conducting;I33b remains non-conducting.

It will be obvious to-one skilled in theart that if a condition isassumed at which triode I332) is conducting, a stable condition resultswherein I33a is non-conducting.

The alternate stability of the multivibrator may be selectivelycontrolled by appropriate application of control voltages to terminalsI42, and l43a or I431). The magnitude of the energizing voltages appliedto each of the triodes through the resistance of paths described is sochosen that with no potentials applied to terminals I42, I43a and I 43b,the grid circuit potential of the conducting triode exceeds thesaturation value of the triode by a magnitude greater than some value:12. Similarly, the grid circuit potential of the non-conducting triodefalls below the cut-off value by a magnitude greater than '0. If thesecircuit conditions are satisfied, the application of either positive ornegative voltages having a magnitude equal to v or less to terminalsI43a. and I43b will not disturb the stable condition of themultivibrator. On the other hand, application of a positive or anegative voltage to terminal M2 can be such as to change the operatingparameters of the multivibrator circuit to an extent that theapplication of a positive or negative voltage having a value 22, eitherto terminal M311 or to I431), will change the relative stabilitycondition of the multivibrator. Two polarities of voltage may be appliedto terminal I42. If a voltage of the proper magnitude applied to I42 ispositive with respect to ground, the increased positive anode potentialthus applied to both the anodes of triodes I38a. and I381) will changethe grid circuit potential of the non-conducting triode suflicientlythat if a positive voltage, 11, is applied to the grid of thenon-conducting triode,'the latter triode will pass from thenon-conductingto the conducting condition.

By way of example, if triode I330 is-conducting and [33b isnon-conducting, an increased positive anode potential on triode i33bresults from a positive potential or impulse applied to terminal M2. Thegrid circuit potential of triode I331), at which the latter tube mayrise above the cut-off point, will be reduced by the increased anodeoperating potential. If, at the same time the positive voltage or pulseis delivered to terminal I42, a negative voltage of value v is suppliedfrom terminal M32) to the grid of I33?) through the resistance [441), l3312 will remain non-conducting; the relative condition of multivibratorstability remains unaiiected. If, however, with the application of apositive voltage to terminal M2, a positive impulse, v, is applied toterminal 143?), the grid circuit potential of I33?) will reach above thecut-off point, allowing the triode 331) to conduct. The relativemultivibrator stability will be altered; triode 833a becomesnon-conducting, l33b conducting.

The positive pulse supplied to terminal I42 during the original periodwhen triode 13311, was conducting will not, of itself, affect theconditions within triode I33a. Increasing the anode potential of thealready conducting triode 133a will make the grid circuit potential ofthis tube even more remote from the control of voltage pulses applied toterminal 143a. If, however, a negative impulse or potential is suppliedto terminal I42, the grid circuit saturation potential of the conductingtriode will be changed sufficiently to allow a negative voltage, 22, tochange the triode condition from conducting to nonconducting. Thus,assuming that triode (33a is conducting, I331) non-conducting, anegative potential or impulse applied to terminal i i-2 will depress theanode potential of the non-conducting triode to a point that a negativepotential or impulse, 12, applied to the grid circuit of the conductingtriode, will make the triode I330, non-conducting. The multivibratorstability will be altered accordingly. If when the negative impulse isapplied to termnial I42 a positive voltage, 0, is applied to terminal143a,, it follows that no efiect will be rendered on triode I33a as itis already conducting at saturation. Changes in the condition ofmultivibrator stability will be called tripping of the multivibratorcircuit.

It should be noted that the magnitude of impulse or potential applied toterminal I42 required to alter the conditions of stability is muchgreater in the case of a positive voltage than for a negative voltage.This polarity discrimination results from the fact that a negativevoltage supplied to terminal I42 passes through the anode resistance ofthe non-conducting triode to the grid circuit of the conducting triode.This path will not be attenuated by the shunt resistance offered by theinternal anode resistance of the non-conducting triode; manifestly, asthe triode is not conducting, its internal resistance is very high.Conversely, a positive potential applied to terminal I42 passes throughthe anode resistance of the conducting triode to the grid of thenon-conducting triode. This path will be attenuated by the shuntingeffect resulting from the relatively low internal resistance of theconducting triode.

It will be seen that if terminal I42 is supplied from a sourcealternately containing both positive and negative potentials ofapproximate equal magnitude, the multivibrator may be made todiscriminate against the positive potentials. As a result, voltages ofnegative polarity alone can be caused to accomplish the selectingfunction.

The circuit of Fig. 9 may therefore be arranged so that only thenegative pulses supplied to terminal I42 cooperate with pulses suppliedto terminals Him and I431) in selection of multivibrator stabilityconditions. Positive voltages supplied terminal I42 will then remainineffective to control the multivibrator.

Referring again to Fig. 712, it will be seen that the multivibrator gatecircuit described with reference to Fig. 9 is utilized in conjunctionwith the pulses derived from the receiver distributor applied toterminal M2; marking and spacing signal derived from the output ofamplifiers Sid and 9lb, Fig. 7a, are applied discretely to terminals143a and I431).

Output signals from amplifying triodes Sid and 9lb to be found on points9311 and 93b are supplied not only to the oscillator start tubecircuits, as previously described, but are supplied through terminals Mand N of Figs. 7a and 7b to buses [45 and 146, respectively. In carryingsignal continuity between the transmitting circuits of Fig. 6 throughthe amplifier tubes Sla and Slb of Fig. m, it may be shown that for themarking and spacing polarities assumed, a marking line condition resultsin a negative voltage on bus I45 and a positive voltage on bus 146.Conversely, a spacing line condition will result in a positive voltageon bus 545 and a negative voltage on bus H55.

If the energizing circuits and supplying resistances of the individualreceiver gates are chosen to discriminate against positive voltagessupplied from the distributor ring to terminals corresponding to 442, itfollows that only the negative voltages applied to buses M5 and M6 willtrip the receiver gates. Thus, negative voltages developed alternatelyon the marking and spacing buses will trip the multivibrator; thetripping will be timed in accordance with the negative voltage derivedfrom the receiver distributor ring. The voltage delivered to thereceiver gate terminals corresponding to 42 is in the nature oftransient pulses; capacitances l28l32 will dispose of non-transientdistributor voltages. As a marking line condition produces negativepulses only on bus 145, I45 will be called the receiver marking bus.Similarly, as spacing line conditions produce negative pulses on bus I46only, 148 will be called the spacing bus.

The magnitude of negative voltages supplied from the amplifiers 91a andSlb in Fig. 7a is required to be sufficiently large to eifect trippingof the receiver gate tubes when combined with the timed negative pulsesderived from the receiver multivibrator ring. To reach this desiredmagnitude, additional amplifiers may be cascaded with 91a and 9H).

To illustrate the operation of the receiver gate circuits, furtherreference may be made to Fig. 7?). If the signal received during thepreceding distributor cycle left multivibrator tubes I331: and I331) inrespective conducting and non-conducting condition, these stabilityconditions will remain over the duration of this preceding distributorcycle. As the first intelligence segment of the present distributorcycle is reached, the first distributor ring tube H9 will provide anegative pulse through capacitance I28 to the point M2. A negative pulseat point I42 offers the multivibrator or receiver gate an opportunity totrip. At the instant that the distributor offers a tripping possibilityto the multivibrator, either a marking or spacing condition exists atthe k transmission line. if a spacing condition exists,

